A correction system for LED display screen

Abstract

The present application relates to the field of display technology, and discloses a correction system for LED display screens, including: an optical measuring device, used to measure the brightness and color data displayed by the initial gamma code on the LED display screen, and transmit it back to the processor; a processor, used to find the best gamma code for each grayscale closest to the target brightness and color through an automated iterative calculation method, and output the gamma table recording the best gamma code for each grayscale to the gamma table memory, and also used to control the temperature change of the LED during the entire measurement process; an LED driving device, used to map the grayscale value of the input original image with the gamma table in the gamma table memory, obtain the corresponding gamma code and output it to the LED display screen. The system can quickly complete the correction, effectively improve the measurement inaccuracy problem caused by LED temperature drift, optimize the gradient effect limited by the physical limitations of the LED itself, and improve the color accuracy of the LED display screen.

Description

Technical Field

[0001] The invention relates to the field of display technology, and in particular to a correction system for an LED display screen. Background Art

[0002] A light-emitting diode (LED) is an electroluminescent semiconductor element. When powered on, the current passing through the LED element will cause the LED to produce light of different colors. Due to the high brightness, good luminous efficiency, energy saving and environmental protection, long life, high reliability, modular splicing display, and diversified application scenarios of LED, LED display screens have been widely used in many outdoor advertisements, indoor exhibitions, movie studios, TV backlights, lighting, etc. in recent years.

[0003] In practical applications, the grayscale level, that is, the number of grayscale levels, is generally controlled by adjusting the fineness of the LED light brightness. The more grayscale levels there are, the more colors that can be combined and displayed, making the picture more delicate and colorful. At present, full-color LED displays on the market have gradually pursued a color depth level of more than 16 bits, and the brightness of each LED is mainly adjusted by the duty cycle of the LED forward current. The brightness of each grayscale is output through the linear relationship between visual perception brightness and duty cycle. However, the human eye is more sensitive to changes in brightness in the dark than in the bright, so that the brightness and grayscale perceived by the human eye are in a logarithmic curve relationship, indicating that more grayscales are needed at low brightness to express the change in brightness in order to meet the perception characteristics of the human eye compared to high brightness. Due to the physical characteristics of LED lights, there are problems such as color deviation from low brightness to high brightness, color brightness change caused by temperature drift, increasing number of color bits, brightness jump, and inversion, which makes manual calibration of LED displays time-consuming and laborious, and the quality after calibration is unstable. In addition, the luminous intensities of red, green and blue are different, and various color band breaks or color deviations are prone to occur in grayscale gradients.

[0004] In addition, the process of LED electroluminescence not only generates light but also generates heat. The higher the output brightness, the more heat is generated. In addition to affecting the life of the LED, the temperature rise will also cause rapid changes in LED brightness and color deviation, making the data measured by the optical measurement device vary greatly each time, causing automatic adjustment inaccuracy. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a calibration system for LED display screens, which can quickly complete the calibration in a short time, effectively improve the measurement inaccuracy problem caused by LED temperature drift, optimize the gradient effect limited by the physical limitations of the LED itself, and improve the color accuracy of the LED display screen. The specific scheme is as follows:

[0006] A calibration system for an LED display screen includes: an optical measurement device, a gamma table memory, an LED driving device, and a processor; wherein:

[0007] The optical measuring device is used to measure the brightness and chromaticity data displayed on the LED display screen by the initial gamma encoding, and transmit it back to the processor;

[0008] The processor is used to find the best gamma code for each gray scale closest to the target brightness and chromaticity through automatic iterative calculation, and output the gamma table recording the best gamma code for each gray scale to the gamma table memory; and is also used to control the temperature change of the LED during the entire measurement process;

[0009] The gamma table memory is used to store the gamma table;

[0010] The LED driving device is used to map the grayscale value of the input original image with the gamma table in the gamma table memory to obtain the corresponding gamma code, and output it to the LED display screen so that the LED display screen displays the corrected grayscale image.

[0011] Preferably, in the above-mentioned correction system provided by the embodiment of the present invention, the processor includes a white point coordinate correction module, an adaptive low grayscale gamma brightness and chromaticity optimization module, a gamma correction module, an automatic acceleration module and an optical measurement module for suppressing LED temperature rise; wherein,

[0012] The white point coordinate correction module is used to perform white point coordinate correction on each color;

[0013] The adaptive low grayscale gamma brightness and chromaticity optimization module is used to perform adaptive low grayscale gamma brightness and chromaticity optimization processing on low grayscale and calculate the target brightness value of each color and each grayscale;

[0014] The gamma correction module is used to perform gamma correction on each color according to the target brightness value;

[0015] The automatic acceleration module is used for iterative calculation to find the best gamma code for each gray scale closest to the target brightness and color;

[0016] The optical measurement module for suppressing LED temperature rise is used to control the LED blackout or lighting time and change the grayscale measurement sequence to stabilize the temperature change of the LED during the entire measurement process.

[0017] Preferably, in the above-mentioned correction system provided by the embodiment of the present invention, the white point coordinate correction module is specifically used to find the maximum brightness and chromaticity of each color when the highest grayscale corresponds to the maximum brightness, and after substituting the target white point coordinates, the brightness gain ratio of each color is obtained through the color conversion matrix of the XYZ color space, and the maximum brightness of each color is multiplied by the brightness gain ratio of each color to calculate the maximum target brightness of each color.

[0018] Preferably, in the above-mentioned correction system provided by an embodiment of the present invention, the adaptive low grayscale gamma brightness and chromaticity optimization module is specifically used to smooth the transition area between the low grayscale original brightness curve and the standard gamma brightness curve to obtain a smooth gamma brightness curve, and calculate the target gamma value corresponding to each grayscale between the starting grayscale and the ending grayscale in the adaptive low grayscale transition area, and calculate the target brightness value of each color and each level according to the calculated target gamma value and the maximum target brightness of each color.

[0019] Preferably, in the correction system provided in the embodiment of the present invention, the adaptive low grayscale gamma brightness and chromaticity optimization module is specifically used to calculate the target gamma value corresponding to each grayscale between the starting grayscale and the ending grayscale in the adaptive low grayscale transition zone using a circle formula or an ellipse formula.

[0020] Preferably, in the above-mentioned correction system provided by the embodiment of the present invention, the adaptive low grayscale gamma brightness and chromaticity optimization module is specifically used to determine the starting grayscale of the adaptive low grayscale transition zone through the relationship between the arc and the tangent, and to find the minimum grayscale closest to the set standard gamma value as the end grayscale of the adaptive low grayscale transition zone through node interpolation or actual iterative measurement, and is specifically used to directly set the starting grayscale value and the end grayscale value by the user.

[0021] Preferably, in the above-mentioned correction system provided by an embodiment of the present invention, the automatic acceleration module is specifically used to calculate the actual brightness measured by each gamma encoding value through an iterative bilinear interpolation formula until the error between the actual brightness and the target brightness meets the standard, the error between the actual gamma value corresponding to the actual brightness and the target gamma value meets the standard, and the error between the actual chromaticity and the target chromaticity meets the standard, so as to find the optimal gamma encoding value for each grayscale that is closest to the target brightness and chromaticity.

[0022] Preferably, in the above-mentioned correction system provided by an embodiment of the present invention, the automatic acceleration module is specifically used to utilize node grayscale sampling for full grayscale to reduce the time required for measuring and calculating full grayscale, and only measure and calculate the node grayscale, and calculate the gamma coding value between the node grayscales through an interpolation formula to obtain the gamma coding value of each grayscale between the node grayscales.

[0023] Preferably, in the correction system provided by the embodiment of the present invention, the gamma table memory is arranged inside the LED driving device.

[0024] It can be seen from the above technical scheme that a correction system for an LED display screen provided by the present invention comprises: an optical measuring device, a gamma table memory, an LED driving device and a processor; wherein the optical measuring device is used to measure the brightness and chromaticity data displayed by the initial gamma code on the LED display screen, and transmit it back to the processor; the processor is used to find the best gamma code for each gray scale closest to the target brightness and chromaticity through an automated iterative calculation method, and output the gamma table recording the best gamma code for each gray scale to the gamma table memory, and is also used to control the temperature change of the LED during the entire measurement process; the gamma table memory is used to store the gamma table; the LED driving device is used to map the grayscale value of the input original image with the gamma table in the gamma table memory, obtain the corresponding gamma code, and output it to the LED display screen, so that the LED display screen displays the corrected grayscale image.

[0025] In the correction system provided by the present invention, the optical measuring device measures the brightness and color data displayed by the initial gamma code on the LED display screen, and transmits it back to the processor, and uses the processor to find the best gamma code for each gray scale closest to the target brightness and color through automatic iterative calculation, and finally outputs the gamma table recording the best gamma code for each scale to the gamma table storage. The LED driving device will output the corrected grayscale image to the LED display screen according to the gamma code in the gamma table, and the processor will control the temperature change of the LED during the entire measurement process, so that the correction can be completed quickly in a short time, effectively improving the measurement inaccuracy problem caused by the temperature drift of the LED, reducing the automatic operation time, optimizing the gradient effect limited by the physical limitations of the LED itself, and greatly improving the color accuracy of the LED display screen. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings required for use in the embodiments or related technical descriptions are briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0027] Figure 1 A schematic diagram of the structure of a correction system for an LED display screen provided by an embodiment of the present invention;

[0028] Figure 2 A schematic diagram of the specific structure of a correction system for an LED display screen provided by an embodiment of the present invention;

[0029] Figure 3 It is the existing standard gamma brightness curve diagram;

[0030] Figure 4Connect the existing original brightness curve to the standard gamma brightness curve;

[0031] Figure 5 A brightness curve diagram after adaptive low grayscale gamma optimization provided by an embodiment of the present invention;

[0032] Figure 6 An adaptive low grayscale gamma brightness curve diagram provided by an embodiment of the present invention;

[0033] Figure 7 A schematic diagram of calculating target gamma values ​​of each grayscale in a transition area by using tangent lines and circles provided by an embodiment of the present invention;

[0034] Figure 8 A schematic diagram of calculating target gamma values ​​of each grayscale in a transition region by using tangent lines and ellipses provided in an embodiment of the present invention;

[0035] Fig. 9 A flowchart of iterative calculation of an automated acceleration module provided by an embodiment of the present invention;

[0036] Fig.10 A schematic diagram of the degree to which the grayscale of an existing LED changes with time and temperature;

[0037] Fig.11 A schematic diagram of the degree of brightness change of the existing LED grayscale over time;

[0038] Fig.12 A schematic diagram showing the degree to which the highest grayscale of an existing LED changes with time and temperature;

[0039] Fig.13 A schematic diagram showing the degree of brightness change of the highest grayscale of existing LEDs over time;

[0040] Fig.14 A schematic diagram of the sequence of optical measurement of a temperature-controlled grayscale mapping table provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] The present invention provides a correction system for an LED display screen, such as Figure 1 As shown, it includes: an optical measuring device 1, a gamma table memory 2, an LED driving device 3, and a processor 4; wherein,

[0043] The optical measuring device 1 is used to measure the brightness and color data displayed on the LED display screen 5 by the initial gamma encoding, and transmit it back to the processor 4;

[0044] Processor 4, used for finding the best gamma code of each gray scale closest to the target brightness and chromaticity through automatic iterative calculation, and outputting the gamma table recording the best gamma code of each gray scale to gamma table memory 2;

[0045] A gamma table memory 2, used for storing a gamma table;

[0046] The LED driving device 3 is used to map the grayscale value of the input original image with the gamma table in the gamma table memory 2 to obtain the corresponding gamma code, and output it to the LED display screen 5 so that the LED display screen 5 displays the corrected grayscale image.

[0047] In the above-mentioned correction system for LED display screens provided by the embodiment of the present invention, the optical measuring device 1 measures the brightness and color data displayed by the initial gamma code on the LED display screen 5, and transmits it back to the processor 4, and uses the processor 4 to find the best gamma code for each grayscale that is closest to the target brightness and color through automatic iterative calculation, and finally outputs the gamma table recording the best gamma code for each level to the gamma table storage 2, and the LED driving device 3 will output the corrected grayscale image to the LED display screen 5 according to the gamma code in the gamma table, and the processor will control the temperature change of the LED during the entire measurement process, so that the correction can be completed quickly in a short time, effectively improving the measurement inaccuracy problem caused by LED temperature drift, reducing the automatic calculation time, optimizing the gradient effect limited by the physical limitations of the LED itself, and greatly improving the color accuracy of the LED display screen 5.

[0048] It should be noted that gamma refers to the smoothness of the transition from low-brightness grayscale to high-brightness grayscale on a digital display. Gamma Code can distribute the degree of grayscale to brightness change according to human perception of light or black and white. Different ambient lights use different gammas. Generally, a higher brightness is required to see clearly in high-brightness ambient light. At this time, the gamma value needs to be lowered. In low-brightness environments, a higher gamma value is required to have more grayscales to express delicate changes in brightness.

[0049] The present invention is applicable to various types of LED display screens, including pulse width driven LED display screens, pulse driven LED display screens, and DC driven LED display screens. Therefore, the gamma coding value recorded by the gamma table in the present invention is exactly the coding value corresponding to the LED driving mode. For example, the gamma coding value used by the pulse width driven LED is the duty cycle.

[0050] In specific implementation, in the correction system provided in the embodiment of the present invention, as Figure 2As shown, the gamma table memory 2 may be arranged inside the LED driving device 3 , that is, the LED driving device 3 has the gamma table memory 2 .

[0051] In specific implementation, in the correction system provided in the embodiment of the present invention, as Figure 2 As shown, the processor 4 may include a white point coordinate correction module, an adaptive low grayscale gamma brightness and chromaticity optimization module, a gamma correction module, an automatic acceleration module, and an optical measurement module for suppressing LED temperature rise; wherein,

[0052] White point coordinate correction module, used to perform white point coordinate correction on each color;

[0053] Adaptive low grayscale gamma brightness and chromaticity optimization module, used to perform adaptive low grayscale gamma brightness and chromaticity optimization processing on low grayscale and calculate the target brightness value of each color and grayscale;

[0054] Gamma correction module, used to perform gamma correction on each color according to the target brightness value;

[0055] Automatic acceleration module, used for iterative calculation to find the best gamma encoding for each grayscale that is closest to the target brightness;

[0056] The optical measurement module that suppresses LED temperature rise is used to control the LED blackout or lighting time and change the grayscale measurement sequence to stabilize the temperature change of the LED during the entire measurement process.

[0057] In practical applications, the white point is defined by the color coordinates as the target white that the LED is to display. According to the type of LED display, if it is a monochrome screen, no white point coordinate correction is performed, only gamma brightness correction and adaptive low grayscale gamma brightness correction are performed. The format in the gamma table only records the best gamma encoding PWM for each grayscale level. W (S); If it is a three-color screen, white point coordinate correction, gamma correction and adaptive low grayscale gamma brightness and chromaticity correction can be performed. The format in the gamma table records the optimal gamma encoding PWM corresponding to each color and each level. R (S), PWM G (S), PWM B (S) The present invention can greatly save manpower and time through white point coordinate correction, gamma correction and adaptive low grayscale gamma brightness and chromaticity correction, and is conducive to the correction management of each display screen.

[0058] Specifically, the parameters used in the white point coordinate correction module, the adaptive low grayscale gamma brightness and color optimization module, the gamma module, and the automatic acceleration module of the present invention may include the standard gamma value stdGma, the total number of grayscales K, the total number of nodes N, the maximum duty cycle value PWM max , minimum duty cycle value PWM min, first grayscale brightness L w (1) = L min , Maximum grayscale brightness L w (K-1) = L max 、Target white point coordinates (tW x , tW y ), maximum gamma error errGma max 、Maximum brightness error errL max And the maximum chromaticity error errC max The number of colors corrected by the present invention depends on whether the LED display screen is an RGB LED or a white light LED type.

[0059] The first stroke starts with the highest grayscale (such as S max =K-1=255), set the highest grayscale brightness as the target brightness at this time tL(K-1)=L max If it is an RGB LED type, the relationship between gamma coding and brightness is calculated iteratively in the automated acceleration module to find the R, G, B gamma coding that matches the optimal target brightness of this grayscale (such as PWM R (K-1), PWM G (K-1), PWM B (K-1)), and measure the gamma encoding to obtain the actual color brightness (x, y, L) of R, G, B, and W, which are (R x (K-1),R y (K-1),L R (K-1))、(G x (K-1),G y (K-1),L G (K-1))、(B x (K-1), B y (K-1),L B (K-1))、(W x (K-1),W y (K-1),L W (K-1)); Input the actual color brightness values ​​of R, G, B, and W into the white point coordinate correction module for calculation, obtain the color splitting ratios gnR, gnG, and gnB of each color of R, G, and B, and calculate the maximum target brightness tL of each color color (K-1) = L color (K-1)×splitting ratio; if it is a white light LED type, then each time the gamma code of W is input to the automatic acceleration module, the gamma code (such as PWM) that matches the best target brightness and color of this grayscale is quickly found. W (S)). According to the standard gamma formula, input the maximum target brightness of each color after white point coordinate correction tL color( K-1), current grayscale S, maximum grayscale Smax , standard gamma stdGma, will be able to calculate the target brightness tL(S) of each level after white point coordinate correction, thus establishing a standard gamma brightness curve after white point correction. Then the gamma encoding value in the automatic acceleration module is iterated to find the R, G, B gamma encoding (such as PWM) that matches the best target brightness and chromaticity of this grayscale. R (K-1), PWM G (K-1), PWM B (K-1)), continuously iterate the white point coordinate correction of this order to calculate the target brightness value of each color and each order until the best gamma code closest to the target brightness and color of each grayscale is found; then the best gamma code and its brightness and color value are recorded in the memory.

[0060] Furthermore, in specific implementation, in the above-mentioned correction system provided in the embodiment of the present invention, the white point coordinate correction module can be specifically used to find the maximum brightness and chromaticity of each color when the highest grayscale corresponds to the maximum brightness, and after substituting the target white point coordinates, the brightness gain ratios gnR, gnG, and gnB are obtained through the 3x3 color conversion matrix of the XYZ color space, and the maximum brightness of each color is multiplied by the brightness gain ratio of each color to calculate the maximum target brightness of each color.

[0061] Specifically, after obtaining the actual color brightness (R x (K-1),R y (K-1),L R (K-1))、(G x (K-1),G y (K-1),L G (K-1))、(B x (K-1), B y (K-1),L B (K-1))、(W x (K-1),W y (K-1),L W (K-1)), the target white point coordinates (tW x ,tW y ) and the above-mentioned actually measured R, G, B, W color brightness values ​​are used to perform the highest-order white point coordinate correction operation. The XYZ matrix corresponding to the target white point coordinates is calculated as:

[0062]

[0063] And the actual XYZ color transformation matrix aM:

[0064]

[0065] Calculate the actual XYZ color conversion inverse matrix aM- 1, calculate the color gain ratio matrix gnM as follows:

[0066]

[0067] Multiply the color gain ratio of R, G, and B by the highest order actual brightness (i.e., the maximum brightness of each color) to obtain the highest order target brightness (i.e., the maximum target brightness of each color) after white point adjustment, which is tL R (K-1) = gnR × L R (K-1), tL G (K-1) = gnG × L G (K-1), tL B (K-1) = gnB × L B (K-1), where K is the total number of grayscales and K-1 is the highest grayscale.

[0068] In addition, the white point coordinate correction module of the present invention can also be used to establish the R, G, B standard gamma brightness curve after white point coordinate correction, and calculate the input standard gamma stdGma and the maximum target brightness tL according to the following formula (i.e., standard gamma formula): R (K-1), tL G (K-1), tL B (K-1), get the target brightness tL of each order R (S), tL G (S), tL B (S), as shown in the following formula:

[0069] color∈R, G, B, s=1~K-1.

[0070] The method for establishing the above-mentioned R, G, B standard gamma brightness curve after white point coordinate correction is not limited to the standard gamma formula, and a user-defined brightness curve can also be used as the standard gamma brightness curve.

[0071] Furthermore, in the specific implementation, in the above-mentioned correction system provided by the embodiment of the present invention, the adaptive low grayscale gamma brightness and chromaticity optimization module can be specifically used to smooth the transition area between the low grayscale original brightness curve and the standard gamma brightness curve to obtain a smooth gamma brightness curve, and calculate the target gamma value corresponding to each grayscale between the starting grayscale and the end grayscale in the adaptive low grayscale transition area, and calculate the target brightness value of each color and each level according to the calculated target gamma value tGma(S) and the maximum target brightness of each color. color∈R, G, B, S=1~K-1.

[0072] It should be noted that, due to the physical characteristics of LEDs, the starting brightness of LEDs at low brightness is higher than the starting brightness of the standard gamma brightness curve, making it impossible to apply the standard gamma brightness curve as the target brightness for low grayscale. The brightness corresponding to the gamma coding used at low brightness is not necessarily presented in a linear manner, that is, the gamma coding at low brightness may not be accurate enough to represent the low-brightness line segment of the standard gamma brightness curve, indicating that the target gamma value of the standard gamma brightness curve at the low-brightness line segment must be revised. If not corrected, no applicable gamma coding can be driven, which can easily cause problems such as gradient flattening, faults, and color bands at low brightness. In the prior art, the industry generally uses the standard gamma correction method to directly use gamma coding = duty cycle = grayscale to make a linear curve mapping at low grayscale, or to use a multi-segment linear brightness curve for low grayscale. The medium and high grayscale are roughly in line with the standard gamma correction method. Figure 3 The standard gamma brightness curve shown in the figure will cause a discontinuous change in the brightness climbing slope, and eventually there will be problems of gradual light and dark bands and color bands near the junction of the linear curve and the standard gamma curve, such as Figure 4 As shown, grayscale 1 to 18 is the brightness curve of the original duty cycle display, and grayscale above 18 uses the standard gamma brightness curve. Figure 4 Although the physical characteristics of LEDs are solved, the low brightness and bright brightness make them unusable. Figure 3 The problem with the standard gamma brightness curve is that the brightness curve at the junction is not smooth, and the discontinuous brightness rise speed will cause a visual perception of gradual light and dark bands.

[0073] The adaptive low grayscale gamma brightness and chromaticity optimization module of the present invention can find the best transition zone brightness curve between the original brightness curve and the standard gamma brightness curve through automatic iterative calculation, and finally obtain Figure 5 The gamma brightness curves shown are all smooth from the onset to the high brightness. That is, the present invention can perform adaptive low grayscale gamma curve correction according to the actual original brightness curve of the LED and the standard gamma brightness curve at low brightness, and use an automated iteration method to approximate the best gamma encoding value of each order closest to the target brightness, and obtain the best smoothed gamma brightness curve of R, G, B, and W from low brightness to high brightness. Finally, the LED display screen will display a gradient effect with a delicate and smooth feeling.

[0074] like Figure 6As shown, p1 is the starting point of the standard gamma brightness curve, p2 is the starting point of the original brightness curve, p4 is the intersection of the original brightness curve and the standard gamma curve, p3 is the starting point of the transition from the original brightness curve to the standard gamma brightness curve, and p5 is the end point of the transition from the original brightness curve to the standard gamma brightness. Line segment p2 to p4 is the original brightness curve, and the duty cycle of each grayscale in this line segment directly corresponds to each grayscale value (PWM=S). The minimum duty cycle that the LED driver can use to light up the LED lamp is 1, so the lowest grayscale S=PWM=1. The original brightness of the LED measured by the optical measurement device p2 is much higher than the standard gamma brightness p1, indicating that the LED driver cannot output the duty cycle required to achieve the standard brightness. The duty cycle that cannot meet the standard gamma brightness will continue to extend to another duty cycle, such as in Figure 6 The brightness of the middle grayscale S=1 to 16 is the original brightness of the LED driver output PWM=1 to 16. It is not until grayscale 16 that the brightness p4 calculated in accordance with the standard gamma formula is connected. Segments p1 to p5 are standard gamma brightness curves, and the duty cycle of each grayscale in this segment is obtained after the aforementioned automatic gamma and white point coordinate correction. However, between segments p1 and p4, due to the physical characteristics of the LED, no corresponding duty cycle can be achieved. The adaptive low grayscale gamma optimization method of the present invention can generate a smooth brightness curve such as segment p3 to p5, and then the duty cycle of each grayscale in the segment is found through automatic gamma and white point coordinate correction, so that all the final grayscale gradients will present a natural and continuous good visual effect.

[0075] In the specific implementation, in the above-mentioned correction system provided by the embodiment of the present invention, the adaptive low grayscale gamma brightness and chromaticity optimization module can also be used to determine the starting grayscale of the adaptive low grayscale transition zone through the relationship between the arc and the tangent, and find the minimum grayscale S closest to the set standard gamma value tGma through node interpolation or actual iterative measurement as the end grayscale S of the adaptive low grayscale transition zone. end , specifically, it can also be used for the starting grayscale value and the ending grayscale value set directly by the user.

[0076] It is understandable that when performing adaptive low grayscale gamma brightness and chromaticity optimization, it is not necessary to use a temperature-controlled grayscale mapping table, because the module operates at low grayscale, and the temperature change at low brightness is low and will not cause inaccurate color brightness measurement. After the grayscales corresponding to all nodes are found by the gamma correction module to find the best gamma encoding and record the actual color brightness value, the adaptive low grayscale gamma brightness and chromaticity optimization operation will be performed, and the actual gamma value Gma(S) corresponding to the actual brightness L(S) of the current level will be calculated. Through node interpolation or actual iterative measurement, the minimum grayscale S closest to the standard gamma value tGma is found as the end grayscale S of the adaptive low grayscale gamma brightness transition zone. end .

[0077] Then measure and record the gamma code value from 1 to the actual gamma value corresponding to the actual brightness, and stop when it is equal to the standard gamma value. The gamma code value at this time is defined as the grayscale S where the original brightness curve and the standard gamma brightness curve intersect. jnc =PWM color (i) The starting grayscale S of the adaptive low grayscale transition zone can be calculated using the original brightness curve, the standard gamma brightness curve, the circle formula or the ellipse formula. str Level, starting grayscale S str To the end grayscale S end The target gamma value tGma(S) corresponding to each grayscale between grayscale 1 and grayscale S. str The original brightness curve is between the two. The gamma encoding value of each grayscale in this area is exactly the grayscale value, which can be directly recorded in the gamma table. str To the end grayscale S end The target brightness tL(S) is calculated based on the target gamma value tGma(S) of each grayscale, and then the gamma code value in the automatic acceleration module is iterated to find the R, G, B gamma code (such as PWM) that matches the best target brightness of this grayscale. R (S), PWM G (S), PWM B (S)), the target brightness value of each color and each level is calculated by continuously iterating the white point coordinate correction until the best gamma code closest to the target brightness is found for each gray level and recorded in the gamma table. Because the original brightness curve is not really linear, it is necessary to gradually find the best starting gray level from gray level 1, and then find the best adaptive low gray level transition zone curve. Through the calculation of the entire automatic gamma and white point coordinate correction, the best gamma code value of each level is found and stored in the gamma table storage device.

[0078] In specific implementation, in the above-mentioned correction system provided by the embodiment of the present invention, the adaptive low grayscale gamma brightness and chromaticity optimization module can be specifically used to calculate the target gamma value corresponding to each grayscale between the starting grayscale and the ending grayscale in the adaptive low grayscale transition zone using a circle formula or an ellipse formula.

[0079] In order to solve the problem that the standard gamma brightness value cannot be used as the target brightness value for low grayscale due to the physical characteristics of LEDs, the present invention calculates the difference between the actual gamma value Gma(S) of each level and the standard gamma value stdGma to find the end grayscale S of the transition zone of the adaptive low grayscale gamma curve. end .like Figure 7 As shown, the horizontal direction is grayscale S = x, the vertical direction is Gamma = y, and the relationship between the arc and the tangent Calculate the starting grayscale S of the transition zone of the adaptive low grayscale gamma curve str =xa. Radius The circle formula is (x-xc) 2 +(y-yc) 2 =r 2 , using the circle formula to calculate the adaptive low grayscale transition area from grayscale S str To Gray Scale S end The target gamma values ​​corresponding to each grayscale are as follows:

[0080] Right now

[0081]

[0082] The adaptive low grayscale gamma encoding brightness and chromaticity optimization method is to set up the adaptive low grayscale gamma curve from the grayscale S str To Gray Scale S end In addition to using the circle formula to calculate the target gamma value, the ellipse formula can also be used to calculate the target gamma value tGma(S) in the transition zone. Using the ellipse formula To calculate the adaptive low grayscale transition area from grayscale S str To Gray Scale S end The gamma value Gma(S) corresponding to each grayscale between Figure 8 As shown, the target gamma value of each grayscale in this area is obtained as t_Gma(S)=Gma(S).

[0083] Furthermore, in a specific implementation, in the above-mentioned correction system provided in an embodiment of the present invention, the automated acceleration module can be specifically used to calculate the actual brightness measured by each gamma encoding value through an iterative bilinear interpolation formula until the error between the actual brightness and the target brightness meets the standard, the error between the actual gamma value corresponding to the actual brightness and the target gamma value meets the standard, and the error between the actual chromaticity and the target chromaticity meets the standard, so as to find the optimal gamma encoding value for each grayscale that is closest to the target brightness and chromaticity.

[0084] Specifically, Fig. 9 The iterative process of calculating bilinear interpolation to approximate the target brightness is shown. Here, the number of times the optical measuring device measures in the process of finding the optimal duty cycle of the current order is defined as the i-th time (or the number of times the duty cycle value is input to the display device), and the duty cycle value input to the display device last is defined as PWM i-1 , when the duty cycle value input to the display device is PWM i , estimate the duty cycle value of the next input to the display device is PWM i+1 , the actual brightness measured last time is L i-1 , when the actual brightness is measured to be L i , when the actual chromaticity measured is (Cx i ,Cy i), the target brightness of this order is tL i , predict the next target brightness to be the current target brightness tL i+1 =tL(S), predict PWM by bilinear interpolation calculation i+1 =PWM i-1 +(tL i -L i-1 )×(PWM i -PWM i-1 ) / (L i -L i-1 ). Each measurement updates the PWM i-1 =PWM i , PWM i =PWM i+1 , L i-1 =L i , and then measure the new PWM i The updated L i As the input for the next iteration. According to the input target gamma value tGma(S) and target brightness tL(S), as well as the actual brightness L i The corresponding actual gamma value Gma i , calculate the actual gamma Gma i The gamma error errGma between the target gamma tGma(S) i , actual brightness L i The error errL between the target brightness tL(S) i , the actual chromaticity and target white point coordinate error errCx i 、errCy i . Through tolerance calculation, check whether the current gamma error and brightness error meet the gamma value maximum error errGma max 、Maximum brightness error errL max and the maximum chromaticity error errC max Limitation. Since the brightness error meets the standard but the chromaticity error does not meet the standard, the actual color brightness measured by the gamma encoding will be corrected by the white point coordinate calculation to redefine the target brightness tL of each color of this order. R (S) = gnR × L R (S), tL G (S) = gnG × L G (S), tL B (S) = gnB × L B (S) is then substituted into the iterative bilinear interpolation formula to predict the gamma code value to be measured next time.

[0085] If the brightness and chromaticity error limits are met, the current duty cycle value is found from the existing records to find the best duty cycle value and output it to the gamma table for storage; if the brightness does not meet the requirements, bilinear interpolation is performed to obtain the next PWM i , the optical measuring device measures the i=i+1th time until all the judgment conditions of the loop are met, then stop looking for the best duty cycle PWM of this order; if the brightness meets the requirements but the chromaticity does not, first calculate the gain matrix gnM through the white point coordinate correction, and then calculate the actual brightness L of the current color i Multiply by the gain value to get the new target brightness tL(S) i , and then perform bilinear interpolation to obtain the predicted PWM i+1 , the optical measuring device measures the i=i+1th time until the judgment conditions of the loop are met, and then stops looking for the best duty cycle PWM of this order. The automatic correction module of the present invention can use bilinear interpolation calculation to predict the best duty cycle, and correct each predicted duty cycle value to see if it is closer to the target brightness through loop iteration measurement and calculation, and finally achieve a fast approach to the best duty cycle, which can improve the accuracy of the actual brightness and the actual white point coordinates from the target requirements.

[0086] It should be noted that the optimal duty cycle required for the brightness of each R, G, B target color can be found for the R, G, B standard gamma brightness curve with the white point coordinates adjusted. Fig. 9 The iterative bilinear interpolation calculation finds the optimal duty cycle PWMR(S), PWMG(S), PWMB(S) required for each order of R, G, B target brightness, and at the same time calculates the actual gamma value GmaR(S), GmaG(S), GmaB(S) of the order by the following formula:

[0087] Color∈R,G,B.

[0088] In the specific implementation, in the above-mentioned correction system provided by the embodiment of the present invention, the automated acceleration module is specifically used to utilize node grayscale sampling for the full grayscale to reduce the time required for measuring and calculating the full grayscale, and only measure and calculate the node grayscale, and calculate the gamma coding value between the node grayscales through the interpolation formula to obtain the gamma coding value of each grayscale between the node grayscales.

[0089] It should be noted that LED displays often improve image quality by increasing color depth, but the increase in grayscale levels will prolong the calibration time. The automatic acceleration module in the present invention uses the customized measurement node settings and the node gamma encoding in the gamma table to interpolate and restore the full grayscale, effectively reducing the overall calibration time. The automatic acceleration module can optimize the automatic speed according to the number of iterations set for each node grayscale.

[0090] Furthermore, since the general automatic gamma correction does not take into account the problem of inaccurate measurement of the optical measurement device caused by the temperature rise of the LED, and the calculation process is mostly calculated in a continuous grayscale manner from low grayscale to high grayscale or from high grayscale to low grayscale, as the grayscale of the lighting continues to rise, the LED will gradually accumulate and heat up over time, or the grayscale of the lighting continues to decrease, causing the LED to gradually cool down over time, which makes the same gamma encoding used but measured at different times have different measurement data, resulting in great differences in the data measured by the optical measurement device each time. Therefore, in the specific implementation, the processor 4 uses the optical measurement module that suppresses the temperature rise of the LED to control the LED black insertion or lighting time and change the grayscale measurement order to achieve the action of stabilizing the temperature, so that the measured data has reference accuracy.

[0091] It should be noted that the general LED gamma and white point coordinate correction does not take into account the problem of LED temperature rise and bright chromaticity drift caused by continuous lighting of high grayscale, which makes the measured data inaccurate and causes unsatisfactory automatic correction results. The present invention proposes a method for suppressing temperature rise to change the order of measuring grayscales, as well as control the time of inserting black or lighting LEDs during the calculation process, which can improve the above-mentioned problems caused by temperature rise caused by continuous lighting of high grayscale. The optical measurement module that suppresses LED temperature rise will set the LED display screen to enter a black screen when the processor is performing calculations to suppress temperature rise, but it can also control the duration of the black screen after the calculation of each level through external parameter input.

[0092] from Fig.10 and Fig.11 It can be seen that the temperature and brightness decay of the LED grayscale have almost no change over time, Fig.12 The temperature of the highest grayscale is 25℃ when it is just lit, until the temperature rises rapidly before time T. Fig.13 Relatively speaking, the brightness change before time T is also large; after time T, the temperature change is small, and the brightness change at this stage is also small, but it is still affected by temperature and continues to decline, but it still affects the brightness and color accuracy. The temperature rise suppression module mainly deals with the impact of temperature changes on brightness after time T, and balances the temperature control by changing the measured grayscale sequence to achieve stable brightness changes.

[0093] Specifically, the parameters used in the optical measurement module of the present invention may include a node grayscale mapping table and a temperature control grayscale mapping table. The present invention uses the order of changing the grayscale lighting to balance the temperature during the entire measurement process, and in order to prevent the LED from accumulating temperature due to continuous lighting of the screen during the waiting time for software calculation, this problem is avoided by controlling the LED blackout or lighting time. The temperature control grayscale mapping table of the optical measurement module is shown in Table 1 below, and the total number of grayscales K = 256.

[0094] Table 1

[0095]

[0096] Since the temperature of LED will rise when it is at high brightness, which will change the luminous efficiency of LED, the brightness and color measured by the optical measurement device at different time points for the same set of duty cycles will drift and cause measurement inaccuracy. Generally, the measurement of full grayscale will increase by 1 grayscale from grayscale 1 to grayscale 255, or vice versa, decrease by 1 grayscale from grayscale 255 to grayscale 1. However, such continuous measurement will cause measurement inaccuracy at high grayscale due to continuous temperature accumulation. If high brightness (higher grayscale) is continuously measured during the automatic calibration process, the calibration will fail due to measurement inaccuracy due to temperature drift. The optical measurement module for suppressing LED temperature rise proposed by the present invention mainly provides users with the best grayscale measurement sequence to reduce the brightness and color drift problem caused by LED temperature rise. This method can reduce the color brightness drift problem caused by temperature accumulation by directly displaying relatively bright and dark levels in turn without increasing the measurement time. See Table 1. The full grayscale is divided into 16 groups. The first grayscale in the first group is 255, the highest grayscale. The grayscale value of the last grayscale value in the first group is 15. The second group is the highest grayscale of the first group minus 1 level. After that, the grayscale is measured every 16 levels until the lowest grayscale of the first group minus 1 level, and so on to the 16th group. The overall temperature is balanced by the average measurement of 16 groups and the low grayscale in each group. The color and brightness data measured at the end can be close to the data measured after the display is turned on at a constant temperature. Fig.14 The diagram is a schematic diagram of the grayscale measurement sequence of the temperature-controlled grayscale mapping table. The grayscale sequence in the temperature-controlled grayscale mapping table can also be determined by the user's simulation of the approximate LED temperature change in advance to determine the order of grayscale measurement in the table.

[0097] In the present invention, the target gamma calculation source can be divided into three major areas according to the grayscale area, namely, the original brightness and chromaticity area (grayscale S = PWM), the adaptive low grayscale gamma brightness and chromaticity optimization area, and the standard gamma white point area. Table 2 lists the calculation methods of the target gamma values ​​tGma(S) of all R, G, and B full grayscales.

[0098] Table 2

[0099]

[0100]

[0101] Finally, the PWM corresponding to each order recorded in the gamma table will be obtained R (S), PWM G (S), PWM B(S), output this gamma table to the storage device in the display, and the driving device can use this gamma table to make the picture display the best effect. In order to speed up the automatic calibration process, after finding the best coding value of each node grayscale, the gamma coding value between each node grayscale is used to establish a complete full grayscale R, G, B gamma table using a bilinear interpolation formula, and finally the gamma table of Table 3 can be obtained, which records the best duty cycle PWM (S) of each grayscale.

[0102] Table 3

[0103]

[0104] It should be pointed out that in the prior art, manual adjustment of gamma and white point coordinates is a time-consuming task. For example, in 8 hours of working time, only 1 to 2 LED display screens can be manually adjusted. In the present invention, the automated correction time is about 1 minute per screen, which effectively solves the difficulty and time-consuming problem of manual screen adjustment. After the correction, the brightness error is no more than 2%, and the chromaticity error is controlled to be no more than 3%, which greatly improves the color accuracy of the LED screen and the smooth and gradient visual effect.

[0105] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0106] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0107] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0108] The correction system for LED display screens provided by the present invention is introduced in detail above. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A calibration system for an LED display screen, characterized in that: include: Optical measuring device, gamma table memory, LED driving device and processor; wherein, The optical measuring device is used to measure the brightness and chromaticity data displayed on the LED display screen by the initial gamma encoding, and transmit it back to the processor; The processor is used to find the best gamma code for each grayscale closest to the target brightness and chromaticity through automatic iterative calculation, and output the gamma table recording the best gamma code for each grayscale to the gamma table memory; it is also used to control the temperature change of the LED during the entire measurement process; the processor includes a white point coordinate correction module, an adaptive low grayscale gamma brightness and chromaticity optimization module, a gamma correction module, an automatic acceleration module and an optical measurement module for suppressing LED temperature rise; wherein, The white point coordinate correction module is used to perform white point coordinate correction on each color; The adaptive low grayscale gamma brightness and chromaticity optimization module is used to perform adaptive low grayscale gamma brightness and chromaticity optimization processing on low grayscale and calculate the target brightness value of each color and each grayscale; The gamma correction module is used to perform gamma correction on each color according to the target brightness value; The automatic acceleration module is used for iterative calculation to find the best gamma code for each gray scale closest to the target brightness and color; The optical measurement module for suppressing LED temperature rise is used to control the LED black insertion or lighting time and change the grayscale measurement sequence to stabilize the temperature change of the LED during the entire measurement process; The gamma table memory is used to store the gamma table; The LED driving device is used to map the grayscale value of the input original image with the gamma table in the gamma table memory to obtain the corresponding gamma code, and output it to the LED display screen so that the LED display screen displays the corrected grayscale image.

2. The correction system according to claim 1, characterized in that: The white point coordinate correction module is specifically used to find the maximum brightness and chromaticity of each color when the highest grayscale corresponds to the maximum brightness, substitute the target white point coordinates, and obtain the brightness gain ratio of each color through the color conversion matrix of the XYZ color space, and multiply the maximum brightness of each color by the brightness gain ratio of each color to calculate the maximum target brightness of each color.

3. The correction system according to claim 2, characterized in that: The adaptive low grayscale gamma brightness and chromaticity optimization module is specifically used to smooth the transition area between the low grayscale original brightness curve and the standard gamma brightness curve to obtain a smooth gamma brightness curve, and calculate the target gamma value corresponding to each grayscale between the starting grayscale and the end grayscale in the adaptive low grayscale transition area, and calculate the target brightness value of each color and each level according to the calculated target gamma value and the maximum target brightness of each color.

4. The correction system according to claim 3, characterized in that: The adaptive low grayscale gamma brightness and chromaticity optimization module is specifically used to calculate the target gamma value corresponding to each grayscale between the starting grayscale and the ending grayscale in the adaptive low grayscale transition zone using a circle formula or an ellipse formula.

5. The correction system according to claim 4, characterized in that: The adaptive low grayscale gamma brightness and chromaticity optimization module is specifically used to determine the starting grayscale of the adaptive low grayscale transition zone through the relationship between the arc and the tangent, and find the minimum grayscale closest to the set standard gamma value as the end grayscale of the adaptive low grayscale transition zone through node interpolation or actual iterative measurement; or, the adaptive low grayscale gamma brightness and chromaticity optimization module is specifically used to directly adopt the starting grayscale value and the end grayscale value set by the user.

6. The correction system according to claim 1, characterized in that: The automated acceleration module is specifically used to calculate the actual brightness measured by each gamma encoding value through an iterative bilinear interpolation formula until the error between the actual brightness and the target brightness meets the standard, the error between the actual gamma value corresponding to the actual brightness and the target gamma value meets the standard, and the error between the actual chromaticity and the target chromaticity meets the standard, so as to find the optimal gamma encoding value for each grayscale that is closest to the target brightness and chromaticity.

7. The correction system according to claim 6, characterized in that: The automated acceleration module is specifically used to utilize node grayscale sampling for full grayscale to reduce the time required for measuring and calculating full grayscale, and only measures and calculates node grayscales, and calculates the gamma coding values ​​of each grayscale between node grayscales through an interpolation formula.

8. The correction system according to claim 1, characterized in that: The gamma table memory is arranged inside the LED driving device.

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